Re: 2.6.26-rc1 regression: ISA DMA broken (bisected)

[Glauber Costa <gcosta@redhat.com>]

Takashi Iwai wrote:
> At Fri, 09 May 2008 03:37:54 +0200,
> Rene Herman wrote:
>> Good day.
>>
>> commit 8779f2fc3b84ebb6c5181fb13d702e9944c16069
>>
>> "x86: don't try to allocate from DMA zone at first"
>>
>> breaks all of ISA DMA. Or all of ALSA ISA DMA at least. All
>> ISA soundcards are silent following that commit -- no error
>> messages, everything appears fine, just silence.
>>
>> It won't just revert due to 32/64 merge.
>>
>> Rene.
> 
> Thanks for catching it.  Yeah, the patch looks buggy.  We had an
> implicit assumption that dev = NULL for ISA devices that require 24bit
> DMA.
> 
> How about the patch below?  It's against the latest Linus git tree.
> 
> 
> thanks,
> 
> Takashi
> 
> 
> [PATCH] x86: Fix dma_alloc_coherent() for ISA devices
> 
> The recent work on x86 dma_alloc_coherent() breaks the ISA DMA buffer
> allocation, which is represented by "dev = NULL" and requires 24bit
> DMA implicitly.
> 
> Signed-off-by: Takashi Iwai <tiwai@suse.de>

Woke up and saw it, got worried, but there is already a fix. ;-)

Nice work! And thank you

> ---
> 
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 0c37f16..c5ef1af 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -385,11 +385,13 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  	if (dma_alloc_from_coherent_mem(dev, size, dma_handle, &memory))
>  		return memory;
>  
> -	if (!dev)
> +	if (!dev) {
>  		dev = &fallback_dev;
> +		gfp |= GFP_DMA;
> +	}
>  	dma_mask = dev->coherent_dma_mask;
>  	if (dma_mask == 0)
> -		dma_mask = DMA_32BIT_MASK;
> +		dma_mask = (gfp & GFP_DMA) ? DMA_24BIT_MASK : DMA_32BIT_MASK;
>  
>  	/* Device not DMA able */
>  	if (dev->dma_mask == NULL)
> @@ -403,7 +405,7 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  	   larger than 16MB and in this case we have a chance of
>  	   finding fitting memory in the next higher zone first. If
>  	   not retry with true GFP_DMA. -AK */
> -	if (dma_mask <= DMA_32BIT_MASK)
> +	if (dma_mask <= DMA_32BIT_MASK && !(gfp & GFP_DMA))
>  		gfp |= GFP_DMA32;
>  #endif
>